1. Field of the Invention
The present invention relates to high-reliability metal sealing materials used in sealing devices of turbines, in particular, steam turbines of combined cycle power plants, conventional thermal power plants, atomic power plants and the like.
2. Background Art
The work efficiency of a steam turbine used in a power generation plant is affected by an amount of a fluid that rotates a turbine blade to generate a motive force (rotating torque); accordingly, performance of a sealing technology that reduces an amount of a fluid leaking from a gap between a stator and a rotor of a turbine determines performance of the turbine. The sealing technology is expected to have a function (abradability) by which even in the worst case where the stator and the rotor come into contact, without damaging both the stator and rotor, only a sealing material is scrubbed and reduced in thickness. Owing to the abradability of the sealing material disposed between the stator and rotor, a gap between the stator and rotor can be reduced to zero without limit, and thereby an amount of a fluid leaking from the gap can be neared zero; accordingly, the work efficiency of the turbine can be largely improved.
As to the sealing technology, in particular, a porous coating layer, for example, JP Published Patent Application No. 61-171969A (1986) discloses a sealing layer made of porous metal (density ratio: 26 to 40%, 60 to 74% in terms of porosity), and, further, discloses to dispose, on the outermost surface portion thereof, a surface layer containing ceramic microparticles to impart corrosion resistance to a working fluid. An object thereof is to prevent “self-erosion” of a sealing material owing to particle detachment from a porous metal sealing material and it is disclosed that the outermost layer containing ceramic microparticles formed on a surface layer exerts its effect of preventing particles from detaching. A target is a turbomachine, but there is no description meaning a steam turbine environment.
In JP Published Patent Application No. 2005-330586A (2005), a metal bond layer of thermal barrier coating (TBC) for gas turbines is formed into a two layer structure having a lower layer and an upper layer, and the upper layer is formed porous (porosity: 3 to 4%) and integrated with a ceramic top layer to improve the heat endurance of the TBC. In this example, in order to alleviate thermal stress, the porosities are gradually varied through the lower layer and upper layer of the metal bond layer and more up to the ceramic top layer. However, there is such a large difference as about 1:10 between thermal expansion coefficients of the ceramic layer and the metal bond layer; accordingly, the thermal stress tends to be increased. JP Published Patent Application No. 2005-330586A (2005) intends to relax thermal stress of a metal bond layer of a thermal barrier coating (TBC) for gas turbines, but not of a metal sealing material of the present invention.
JP Published Patent Application No. 2007-327139A (2007) discloses, as to a ceramic seal, a high temperature sealing material where a dysprosia (Dy2O3)-stabilized zirconia (ZrO2) material (DySZ) that is a top ceramic layer is made porous so as to have the porosity of 15 to 45% and integrated with a dense undercoat metal layer to form a two layer structure and that can be used up to 1200° C. JP Published Patent Application No. 2007-327139A (2007) intends to provide a ceramic sealing material made of a ceramic up to 1200° C., but not of a metal sealing material of the present invention.
JP Published Patent Application No. 09-67662A (1997) discloses, as to a ceramic coating member, a two-layer structure where a top ceramic layer is densified so that the porosity may be 0 to 5% and an underlayer ceramic layer is made porous so as to have the porosity of 20 to 30% to alleviate thermal stress. Similarly to JP Published Patent Application No. 2005-330586 (2005), there is a large difference of about 1:10 between thermal expansion coefficients of the ceramic layer and the metal bond layer; accordingly, a ceramic layer is formed into two layers to alleviate thermal stress. JP Published Patent Application No. 09-67662A (1997) discloses ceramic layers different in porosity to relax thermal stress of a ceramic coating member, but not of a metal sealing material of the present invention.
Concerning the sealing technology, in particular, a porous coating layer, no patent literature has been found concerning a metal sealing material under a steam turbine environment.